Diverse Functions of Oxygen Vacancies for Oxygen Ion Conduction

To elucidate the ion conduction mechanism, the pure oxide structure Sn1–xCexO2−δ (x = 0.05, 0.025) is obtained by doping Ce into SnO2 and combined with Sm0.2Ce0.8O3−δ to form an Sn1–xCexO2−δ–SDC semiconductor-ionic material (SIM), which is evaluated as the electrolyte membrane to assemble fuel cells. Raman measurements revealed that two types of oxygen vacancies, the Frenkel oxygen vacancy (F-OV) and the intrinsic oxygen vacancy (I-OV), simultaneously existed in the Sn1–xCexO2−δ–SDC SIM. Through X-ray photoelectron spectroscopy (XPS) characterization and density functional theory (DFT) calculation, it can be found that I-OVs provide a transport pathway for oxygen ions. In contrast, F-OVs function against the oxygen ion conduction due to the Coulomb repulsion of interstitial oxygen toward oxygen ions. The influence of the Ce doping in SnO2 lies on restraining the production of F-OVs to benefit the oxygen ion conduction and finally improve the electrochemical performance of the assembled fuel cell.